Inkjet printers print dots on a print medium by ejecting small drops of ink from one or more nozzles. Commonly, a number of nozzles are carried on a moveable print head which can be scanned across a surface of the print medium. Each nozzle may be controlled individually to eject a drop of printing fluid, such as ink when commanded. By appropriate control of each nozzle as the print head carrying the nozzles is scanned across the surface of the print media, a desired pattern of printing fluid drops can be deposited on the print medium.
Inkjet printers use a predefined set of “printing modes” where all printing parameters are set by the manufacturer and are static (i.e. do not change with reaction to printer behaviors). Different printing modes may be provided for different types of content to be printed.
Print heads may carry an array of nozzles allowing ink to be deposited in a number of lines of pixels, or a swath, in a single pass of the print head. To allow a full image, consisting of a number of swathes to be deposited on the print medium, the medium is advanced through the printer to allow subsequent swathes to be deposited. Multiple colours of ink may be deposited using a separate nozzle array for each colour of ink, and by controlling the location at which different colour drops of ink according to a mask.
Often, inkjet printers print in a multi pass printing method, where the nozzle array is scanned across each region of the print medium a number of times with ink being deposited on more than one pass of the print head. This is usually done as the scanning array moves in the cross-print (lines) axis between each and every scan. After each pass of the print head the print medium is advanced through the printer by a proportion of the height of a swath such that ink deposited to the same line on the print medium will be delivered by a different nozzle in the nozzle array in a subsequent pass.
This creates a redundancy, where every image line printed has the opportunity to be printed by a different nozzle each time the nozzle array is scanned across the print medium. Fore print mode where an image is printed in “three pass”, every line has three different nozzles that may take place in printing it.
To avoid a situation where a line is printed fully three times (in the above example), typically the line is separated for each nozzle using a mask.